Expanding territory after bonding... or new territory?

So.. fingers crossed my two boys are getting on now...!
Was just wondering about the next step of increasing their territory. I was going to scrub clean the hallway and let them have that too next, and expand it room by room. However, due to big bun's constant desire to explore/claw at closed doors (I'm worried it's making him unhappy being in a small room), I was wondering if there was another way.
What I was thinking was to clean/neutralise the entire flat (everything except the little room they're in now & little buns cage in my room is big buns territory!) and then introduce them together to a new room, as I did with the 'bonding' room. Then do this with each room in turn. The idea behind this was that the flat would become 'their' territory faster, as it would only be one room at a time rather than giving them too much space at once each time another room was opened up.

Does this sound like a good idea?

Any more tips for increasing the space?

I would gradually increase the space as you say and neutralise the rooms. If they start to show signs of aggression decrease it for a couple of days or until they settle again.

You really need to try it and see what happens, it sounds like a good idea to gradually introduce them room by room. Some buns react differently to increase space and it sets them off nipping and chasing, but some just take it in their stride with no fuss.
Good luck.